To determine the role of streptococcal infection in the pathogenesis of guttate psoriasis. Streptococci isolated from patients with guttate psoriasis will be characterized for their exotoxin production. Peripheral blood T cells and skin infiltrates of psoriatic patients will be analyzed for superantigenic effects. Streptococcal pyrogenic exotoxins (SPES) are also tested for their capacity to induce psoriasis directly by patch testing nonlesional skin of patients with psoriasis and normal controls with SPES.